Arya Stark is her first acting job?
She is an amazing child-actor (and I suspect in a few years, an amazing actor). I don't see any other acting credits for her - is Ayra Stark really her first role?
If it is, they took a big risk in casting her as such a major character, but it really paid off! Maisie really excels in this role, and probably will excel in many more in the future!